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.Dd $Mdocdate: September 2 2024 $
.Dt X509_LOOKUP_HASH_DIR 3
.Os
.Sh NAME
.Nm X509_LOOKUP_hash_dir ,
.Nm X509_LOOKUP_file ,
.Nm X509_LOOKUP_mem
.Nd certificate lookup methods
.Sh SYNOPSIS
.In openssl/x509_vfy.h
.Ft const X509_LOOKUP_METHOD *
.Fn X509_LOOKUP_hash_dir void
.Ft const X509_LOOKUP_METHOD *
.Fn X509_LOOKUP_file void
.Ft const X509_LOOKUP_METHOD *
.Fn X509_LOOKUP_mem void
.Sh DESCRIPTION
.Fn X509_LOOKUP_hash_dir ,
.Fn X509_LOOKUP_file ,
and
.Fn X509_LOOKUP_mem
return pointers to static certificate lookup method objects
built into the library, for use with
.Vt X509_STORE .
.Pp
Users of the library typically do not need
to retrieve pointers to these method objects manually.
They are automatically used by the
.Xr X509_STORE_load_locations 3
or
.Xr SSL_CTX_load_verify_locations 3
functions.
.Ss File Method
The
.Fn X509_LOOKUP_file
method loads all the certificates or CRLs present in a file into memory
at the time the file is added as a lookup source.
.Pp
The file format is ASCII text which contains concatenated PEM
certificates and CRLs.
.Pp
This method should be used by applications which work with a small set
of CAs.
.Ss Hashed Directory Method
.Fa X509_LOOKUP_hash_dir
is a more advanced method which loads certificates and CRLs on demand,
and caches them in memory once they are loaded.
As of OpenSSL 1.0.0, it also checks for newer CRLs upon each lookup, so
that newer CRLs are used as soon as they appear in the directory.
.Pp
The directory should contain one certificate or CRL per file in PEM
format, with a filename of the form
.Ar hash . Ns Ar N
for a certificate, or
.Ar hash . Ns Sy r Ns Ar N
for a CRL.
The
.Ar hash
is the value returned by the
.Xr X509_NAME_hash 3
function applied to the subject name for certificates or issuer
name for CRLs.
The hash can also be obtained via the
.Fl hash
option of the
.Xr openssl 1
.Cm x509
or
.Cm crl
commands.
.Pp
The
.Ar N
suffix is a sequence number that starts at zero and is incremented
consecutively for each certificate or CRL with the same
.Ar hash
value.
Gaps in the sequence numbers are not supported.
It is assumed that there are no more objects with the same hash
beyond the first missing number in the sequence.
.Pp
Sequence numbers make it possible for the directory to contain multiple
certificates with the same subject name hash value.
For example, it is possible to have in the store several certificates
with the same subject or several CRLs with the same issuer (and, for
example, a different validity period).
.Pp
When checking for new CRLs, once one CRL for a given hash value is
loaded, hash_dir lookup method checks only for certificates with
sequence number greater than that of the already cached CRL.
.Pp
Note that the hash algorithm used for subject name hashing changed in
OpenSSL 1.0.0, and all certificate stores have to be rehashed when
moving from OpenSSL 0.9.8 to 1.0.0.
.Ss Memory Method
The
.Fn X509_LOOKUP_mem
method supports loading PEM-encoded certificates and revocation lists
that are already stored in memory, using the function
.Xr X509_LOOKUP_add_mem 3 .
This is particularly useful in processes using
.Xr chroot 2 .
.Sh RETURN VALUES
These functions always return a pointer to a static object.
.Sh SEE ALSO
.Xr SSL_CTX_load_verify_locations 3 ,
.Xr X509_LOOKUP_new 3 ,
.Xr X509_STORE_load_locations 3 ,
.Xr X509_STORE_new 3
.Sh HISTORY
.Fn X509_LOOKUP_hash_dir
and
.Fn X509_LOOKUP_file
first appeared in SSLeay 0.8.0 and have been available since
.Ox 2.4 .
.Pp
.Fn X509_LOOKUP_mem
first appeared in
.Ox 5.7 .
